The tomato Solanum lycopersicum (formerly Lycopersicon esculentum) is susceptible to a large number of viral species. Some of the most prominent tomato viruses include Tomato spotted wilt virus (TSWV; genus Tospovirus); Pepino mosaic virus (PepMV; genus Potexvirus), and Tomato yellow leaf curl virus (TYLCV; genus Begomovirus). The damage that these diseases inflict on the plant range from discoloration of leaves and necrotic lesions, to severe crop loss and death of the plant.
The ability to provide resistant plants is of utmost importance to commercial breeders, and for some of the economically most damaging viruses, resistant plant varieties have been produced. However, from time to time, new viruses emerge that may inflict considerable damage on crops.
In 1996 a new tomato virus was reported which had infected tomato plants in the USA and Italy since 1993, and was named Tomato infectious chlorosis virus (TICV; genus Crinivirus; Duffus et al., 1996). Another new tomato virus of the same genus was reported in 1998. This virus was shown to have infected tomato plants in the USA since 1989 and was named Tomato chlorosis virus (ToCV; Wisler et al., 1998). Both these new viruses proved to be spread by a whitefly, the insect being a very effective disease-transmission vector.
It is generally believed that the geographic distribution of known viruses will increase and that new viruses will continue to appear, partly as a result of recombination of different viruses to form new strains or new viruses. The development of resistant cultivars can play an important role in the successful management of these diseases.
Recently, a new virus was discovered on tomato plants from Spain, which caused symptoms (locally known as the disease “torrado”) that could not be attributed to any known virus. The plants exhibited necrotic lesions on leaves and brown rings on fruits and showed reduced growth. Serological tests (ELISA) indicated the presence of Pepino mosaic virus (PepMV). Electron microscopic investigations indeed revealed the rod-like particles typical for potexviruses. However, also spherically shaped viral particles were found in infected leaf tissue. The inventors were able to separate the new virus from the complex with PepMV. The new virus was tentatively named Tomato torrado virus (ToTV), was deposited with the Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH on 24 Nov. 2004 under depositors reference number ToTV-E01 (DSM 16999), and is the causative agent of diseases affecting tomato known as “torrado” (Spain), “marchitez” or “chocolate” (Mexico and Guatemala). It is believed that the virus is also capable of causing disease symptoms which are similar to those caused in tomato in other genera of Solanum, notably in Capsicum spp. (Pepper) and Solanum melongena (Aubergine).
At present there are no plants known that harbour specific resistance to this new virus, while there is a need for developing such resistant plants.